Sensorless control in steer-by-wire application

Abstract

This dissertation presents Sensorless Control as applied to the Steer-by-Wire Application. The steer-by-wire is an integral part of the electrification of automotive vehicles whereby mechanical components are replaced by electronic sensors and electrical actuators. In this by-wire application, the column linking the handwheel and the steered wheel sides is removed and replaced by an electrical machine at each end of the arrangement. The fundamental aim of steer-by-wire is to replicate the input at the handwheel given by the driver to the steered wheels with the minimum delay possible. In order for this to be implemented, robust position measurements at both ends of the system are required. Traditionally, position sensors have been identified as being more prone to failure than other types of electronic transducers. Hence, backup position measurements are typically included in steer-by-wire to ensure the necessary safety levels. In this dissertation, it is proposed that redundant position sensors are replaced by a sensorless algorithm. The algorithm is to be used for the detection of sensor failures and possible changeover to sensorless operation. The steering wheel in an automotive vehicle is typically at rest at the initial position with fast transients while steering. Therefore, a sensorless algorithm for zero speed operation and with sufficient bandwidth to track the position transients is required. From literature, High Frequency-based Sensorless Control was identified as being the most suitable for this application. The magnetic signatures of the Surface-Mounted Permanent Magnet Synchronous Machines used for sensorless control in this dissertation were investigated under different operating conditions, including different transient injection angles, load current and rotor speed. The deviation of the signatures of the experimental machines from the fundamental theoretical models was identified and results for different machine geometries compared. Due to the presence of significant saliency harmonics, an innovative search-based sensorless algorithm was proposed to estimate the speed and position of the experimental machines. The search-based sensorless method was tested in sensorless current, speed and position control systems under dynamic load conditions. The sensorless operation was extended to the steer-by-wire application with typical scenarios investigated for the currentcontrolled handwheel and the position-controlled steered wheel side.